Annealing in Zn Vapours For Manufacturing Large-Aperture Cr:ZnS Laser Gain Media

Transition metal's doped II-VI chalcogenides are unique materials for gain media of ultrafast lasers in 2–6 μm spectral ranges [1]. Among the mentioned compositions the most useful are TM<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup>:ZnS and TM<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup>:ZnSe because of highest thermal stability, biggest life-time of the active ion's excited state and isotropic optical properties. But high melting point makes growing of these materials from melt quite challenging procedure. The useful alternative is a diffusion doping [2]. This process is usually performed at temperatures below 1200 °C and allows to use a robust fused silica as a sealed container, vacuumized or filled with inert gas. On the other hand, the longtime doping process leads to appearing microdefects in the crystalline substrate close to the surfaces because of Zn evaporation and, thus, increased value of losses. Doping bulk substrates with a thickness greater than 3 mm and improving the uniformity of dopant concentration requires higher temperatures and longer processing durations. This intensifies Zn evaporation and increases the thickness of the defective layer. Here we propose a method for healing defective layers.